1. Field of the Invention
The present invention relates generally to sewing machine bobbins, and in particular to an improved core construction for bobbins used in sewing machines utilized to manufacture mattresses and other quilting constructions.
2. Description of the Prior Art
Generally speaking, bobbins for use in sewing machines are known in the art. The function of a bobbin in a sewing machine is to interweave or "lock" the needle thread when the needle passes down through the fabric being sewn by the machine. The bobbin is rotated to pass the needle thread around the bobbin; the needle thread then retracts upwardly through the fabric. Typcial bobbins are disposed in a bobbin case which includes a center post mounted in the case and a pivotable latch mounted on the post, both of which have a combined axial length which is greater than the axial width of the bobbin case. Without a bobbin disposed in the bobbin case, a needle thread passed around the bobbin case would slide off the side thereof and engage the center post of the case. The result of this would be that the thread would catch on the center post and possibly break.
The conventional method of sewing with such sewing machines is to utilize a bobbin having a thread mass wound thereon to an axial thickness which is considerably less than the total height of the post in the center of the bobbin case. After the thread mass is wound on the bobbin to the required height, the operator of the sewing machine presses a pair of metal sides, which are generally circular in shape and have a cylindrical core extending outwardly from one side thereof, onto the bobbin within the inner space of the cylindrical core on which the thread mass is wound. The metal sides of the bobbin case facilitate a smooth transition of the needle thread during sewing from its starting point over the top of the bobbin case, the side of the bobbin, and the latch of the bobbin case. The disadvantage of utilizing such a bobbin is that after winding the thread mass on the core, additional sewing machine operator time is required to assemble and disassemble the bobbin during use. Also, the space taken up by the sides of the bobbin reduces the space available for the thread mass on the bobbin.
In order to enable more thread to be wound on the bobbin, and to avoid the need to assemble and disassemble bobbins with metal sides, it is possible to eliminate the metal sides completely from the bobbin and fill the entire space from the bottom of the bobbin case to the latch of the bobbin case with the thread mass. The disadvantage of this bobbin configuration, however, is that the needle thread interferes with the exposed shoulder of the bobbin thread in most cases and causes the thread to catch and possibly break during sewing.
The type of sewing machines described above are commonly used in the manufacture of mattresses and other quilting constructions. In one such machine, two or three sewing machine heads are utilized and the bobbins are held in the sewing machine in a vertically upward position. In certain models of such machines, as many as 36 bobbins may be required to be changed at one time. Thus, in utilizing such a machine, considerable time may be expended by an operator in assembling and disassembling bobbins with metal sides. In other typical sewing machines, two or three sewing machine heads are utilized but the bobbin case is placed within the machine so that the bobbin and the shuttle thereof are disposed in an upside-down position. Such positioning of the bobbin case increases the possibility that the needle thread and bobbin will interfere with one another during the sewing operation.
There is, thus, a need for a bobbin construction for sewing machines, particularly those used in the manufacture of mattresses and other quilting constructions, which is simple in design and may be efficiently assembled and, in addition, will eliminate interference between the sewing machine needle thread and the bobbin due to the positioning of the bobbin case in the sewing machine.